Maybe this is more strict but safer?
I have a hand-held kitchen timer sort of device that runs directly from 2 AA batteries. I have the BOD disabled. Why? Because I don't care if the battaries can't provide enough energy for the device to run correctly. In the worst case, the thing makes strange noises instead of beeping, flashes an LED erratically, or doesn't keep time. In this case, BOD disabled is perfectly safe1
For an Arduino controlling a very large engine that compresses natural gas for transportation down a pipeline a disabled BOD is certainly NOT safe.
Basically, the processor is guaranteed to function correctly at a certain voltage and clock speed. The BOD should be set based on the clock speed and the circumstances. In other words, only you can decide what's "safer".1
In the sense that no one will be injured. The same can't be said for what's cooking!